1. Field of the Invention
The invention relates to an extrusion blow molding device for producing hollow bodies according to the preamble of claim 1. The invention also relates to a method for producing plastic containers in an extrusion blow molding process.
2. State of the Art
The previously conventional containers made of white or coloured sheet metal, of glass or else of ceramic are increasingly being superseded by containers made of plastic. Mainly plastic containers are used in particular for the packaging of fluid substances, for example of beverages, oil, cleaning utensils, cosmetics, etc. The low weight and the lower costs certainly play a not inconsiderable part in this substitution. The use of recyclable plastics materials and the overall more beneficial total energy balance in the production thereof also help to promote consumer acceptance of plastic containers, in particular of plastic bottles.
Plastic containers, in particular plastic bottles, for example made of polyethylene or polypropylene, are produced by extrusion blow molding, in particular by tube blow molding. In this case, a plastic tube is extruded from an extruder head, introduced into blow molding tools, inflated via an insufflation device, for example a blow mandrel or a blow needle, as a result of excess pressure and cured by cooling. The extrusion blow molding machines used for this purpose generally have at least one extruder for supplying the plastics material. The output of the extruder is connected to the extruder head, from the outlet die of which, the opening width of which can preferably be regulated, the tube, which is extruded in one or more layers, issues. The extruded tube is transferred to a blow molding tool and inflated within the cavity thereof using the insufflation device, for example a blow mandrel or a blow needle. During inflation using a blow mandrel, the neck portion of the plastic bottle is shaped at the same time. A blow needle is used to carry out only an inflation of the plastic tube inserted into the molding cavity. The plastic tube can have one or more layers and can be extruded as a tube with viewing strips, decorative strips or, based on the circumference, with a plurality of, for example different-coloured, segments.
The blowing station with the insufflation device is conventionally arranged laterally of the extruder head and the blow molding tool, which is loaded with the extruded tube, has to be moved into the blowing station, where the insufflation device, for example a blow mandrel, is then introduced, usually from above, into the blow molding cavity. For continuous operation, two blowing stations are conventionally provided in a type of the known extrusion blow molding machines. Each blowing station is equipped with a blow molding tool. The blowing stations are in this case arranged opposing each other at both sides of the extruder and have blow molding tables with the blow molding tools which are moved alternately under the extruder head in order to receive the extruded tube. In this case, the blow molding tool is opened for retrieving the tube. After the blow molding tool has been closed, the tube is separated off between the extrusion head and the blow molding tool. Afterwards, the blow molding table is moved back into the blowing station, where the insufflation device is introduced into the cavity of the blow molding tool and the tube is inflated in accordance with the blow molding cavity and afterwards removed. In multiple extrusion heads and multiple blow molding tools, each blowing station is equipped with a corresponding number of insufflation devices which are jointly introduced into the blow molding cavities. Overall, the extruder with the extruder head and the two blowing stations form roughly the shape of a T. In this case, the extruder with the extruder head is the long stem of the T, whereas the two blow molding tables are alternately movable under the extruder head along the short horizontal line halves.
Extrusion blow molding machines are also known in which a number of blow molding tools are arranged on a rotating wheel. The wheel is positioned roughly vertically and advances the blow molding tools roughly tangentially up to the plastic tube which is continuously extruded from the extruder head. Shortly before reaching the extruded plastic tube, the advanced blow molding tool is opened in order to retrieve the tube. On further rotation of the wheel, the blow molding tool is closed around the inserted tube which is finally sheared off on further rotation. The arrangement of the blow molding tools and the rotational speed of the wheel are selected in such a way that the tube is sheared off only once the subsequent blow molding tool has closed around the next piece of tube. On further rotation of the wheel, the tube, which is located in the cavity of the blow molding tool, finally enters the blowing station, where it is inflated in accordance with the blow molding cavity via an insufflation device introduced laterally into the molding tool. Finally, the inflated hollow body is output from the blow molding tool by opening. During the further movement, the blow molding tool, which is arranged on the rotating wheel, is closed again and advanced back up to the extruder head in order to receive a further extruded tube.
WO 2004/078457 A1 discloses an extrusion blow molding device for producing hollow bodies, in particular plastic bottles, having an extruder head which is arranged in an apparatus frame and has at least one extrusion die, a blow molding tool arrangement with at least one blow molding cavity, at least one insufflation device and at least one separating means. The blow-molding tool arrangement has at its side remote from the extrusion die an orifice through which the insufflation device, which is likewise arranged at the side of the blow molding tool arrangement that is remote from the extruder head, can be introduced into the molding cavity. As a result of the selected arrangement, the extruded plastic tube is held and permanently guided throughout the entire production cycle of a container. In this case, the relative axial distance between the blow molding tool arrangement and the extruder head is altered. Conventionally, this takes place by way of a restrictedly guided axial adjustment of the height of the extruder head in relation to the blow molding tool arrangement during the production cycle. The tube with the fully inflated container is separated off only once the blow molding tool arrangement has closed around a tube portion arranged thereabove. A separating means, which is likewise arranged on the side of the blow molding tool arrangement that is remote from the extrusion die, is provided for separating-off.
In the axial adjustment of the height of the extruder head, large masses have to be moved in relatively short time portions. This results in a comparatively high energy requirement. The exact axial height adjustment is associated with comparatively high control costs. However, the precise orientation and the avoidance of incorrect positioning of the plastic tube, the reproducibility of the production process as a consequence of the use of just a single blow molding cavity and the avoidance of downtimes for lateral adjustment of the blow molding tool arrangement justify these costs. Nevertheless, it is desirable to still further simplify this extrusion blow molding device leading to outstanding results.
A device for producing hollow bodies made of plastic by extrusion blow molding is known from WO 02/081180. The device has an extrusion unit which has an extruder defining a longitudinal direction of the device and an extruder head connected to the extruder and is mounted in a housing frame. At least one blow molding station has a blow molding table with at least one molding tool provided with an opening arranged at the side of the molding tool that is remote from the extrusion die. The molding tool is movable on a lateral path running substantially perpendicularly to the longitudinal direction from an end position laterally of the extruder head into a position under the extrusion head and back again. This allows the extrusion die and the opening of the molding tool to be made to vertically overlap. The extrusion unit is mounted in the housing so as to be vertically inclinable about a horizontal axis and laterally pivotable about a vertical axis and is displaceable in the longitudinal direction. The articulated mounting is formed in the region of the centre of gravity of the extrusion unit, namely at the end region of the extruder that is remote from the extruder head. A drive unit for the extruder is flanged onto the transmission housing as a counterweight to the extruder.
The present invention is therefore provided to simplify an extrusion blow molding device based on a single blow molding tool arrangement, the extruder head being axially adjustable relative to the blow molding tool arrangement, in such a way that the design and control-related costs are reduced. It should likewise be possible to reduce the energy costs for operating the device. In this case, the advantages of the extrusion blow molding device are to be preserved, the extruder head being axially adjustable relative to the blow molding tool arrangement and the extruded plastic tube being permanently guided during the production cycle, and it should still be possible to carry out the extrusion blow molding method in accordance with the principle presented in WO 2004/078457 A1. Furthermore, it should still be possible to arrange even relatively tall blow molding tool arrangements under the extrusion die of the extruder head.